A member of the pea family, licorice root has been used since ancient times both as food and as medicine. In Chinese herbology, licorice is an ingredient in nearly all herbal formulas for the traditional purpose of "harmonizing" the separate herbs involved.

The herb licorice contains a substance called glycyrrhizin. When taken in high enough amounts, glycyrrhizin produces effects similar to those of the natural hormone aldosterone, causing fluid retention, increased blood pressure, and loss of potassium.
1-4
To prevent this, manufacturers have found a way to remove glycyrrhizin from licorice, producing the safer product deglycyrrhizinated licorice (DGL).

What Is Licorice Used for Today?

DGL has shown some promise for the treatment of
ulcers
.
7
Weak evidence hints that it might also help prevent ulcers caused by
anti-inflammatory drugs.
8

Licorice, in the form of a dissolving patch, is also sometimes recommended for relieving the discomfort of
canker sores
and other mouth sores.
29,30

Whole licorice, not DGL, is used as an expectorant for respiratory problems such as
coughs
and
asthma
.

Licorice has been suggested as a treatment for
chronic fatigue syndrome (CFS)
, based on the observation that people with CFS appear to suffer from low levels of certain adrenal hormones. The glycyrrhizin portion of licorice may relieve symptoms by mimicking the effects of these hormones. However, this is a fairly dangerous approach to treatment that should be tried only under medical supervision. In addition, studies of drugs that even more closely imitate adrenal hormones have not found benefit.

Licorice extracts are used intravenously in Japan for treatment of
viral hepatitis
.
27,28
However, there is no definite evidence that this treatment is effective; even if this were established, it would not imply that oral licorice would have a similar effect; furthermore, the high dosages used for treatment of chronic hepatitis may cause an elevation of blood pressure and other serious medical problems.
Warning
:
Do not inject preparations of licorice designed for oral use.

What Is the Scientific Evidence for Licorice?

Eczema

Creams containing whole licorice (often combined with extract of chamomile) are in wide use as "natural hydrocortisone creams." However, there is only preliminary supporting evidence for this use. In one double-blind, placebo-controlled trial of 30 people, licorice gel at 2% was more effective than placebo or 1% gel for reducing symptoms of
eczema
.
22

Licorice has constituents that increase the activity of naturally occurring (or artificially supplied) corticosteroids,
12
and this might explain some of the benefits seen.
In addition, licorice contains licochalcone A, a substance hypothesized to have anti-inflammatory effects.
26

Ulcer Treatment

Two controlled studies suggest that regular use of DGL in a combination product also containing antacids can heal ulcers as effectively as drugs in the Zantac family.
9,10
Unfortunately, these studies do not prove that DGL was effective; antacids themselves can help heal ulcers, and in any case the studies were not
double-blind
. (For information on why this matters, see
Why Does This Database Rely on Double-blind Studies?
)

Furthermore, if it does work, DGL would have to be taken continuously to avoid ulcer recurrence. In some cases, drug treatment can prevent the recurrence of ulcers permanently by eradicating the bacteria
Helicobacter pylori
.
There is no evidence as yet that DGL can do the same.

Ulcer Prevention

A very preliminary study suggests that DGL might help prevent ulcers caused by
aspirin
and related medications (such as ibuprofen).
8

Dosage

For supportive treatment of ulcer pain along with conventional medical care, the standard dose is two to four 380-mg tablets of DGL taken before meals and at bedtime. The same tablets can be allowed to slowly dissolve in the mouth for possible relief of mouth sore pain.

A typical dose of whole licorice is 5 to 15 g daily. However, we do not recommend the use of doses this high for more than a few weeks. For long-term consumption, about 0.3 g of licorice root daily should be safe for most adults. (See Safety Issues.) Individuals who wish to take a higher dose should do so only under the supervision of a physician.

For the treatment of eczema, psoriasis, or herpes, 2% licorice gel or cream is applied twice daily to the affected area.

Safety Issues

Use of whole licorice has not been associated with significant adverse effects in the short term. However, two or more weeks of use may cause high blood pressure, fluid retention, and symptoms related to loss of potassium.
19-21,23
Such effects are especially dangerous for people who take the drug
digoxin
or medications that deplete the body of potassium (such as
thiazide
and
loop diuretics
), or who have high blood pressure, heart disease, diabetes, or kidney disease.

Current evidence indicates that individuals who wish to take whole licorice on a long-term basis without any risk of these side effects should not consume more than 0.2 mg of glycyrrhizin per kilogram of body weight daily.
20
For a person who weighs 130 pounds, this works out to 12 mg of glycyrrhizin daily. Based on a typical 4% glycyrrhizin content, this is the equivalent of 0.3 grams of licorice root.

Whole licorice may have other side effects as well. For example, it appears to reduce testosterone levels in men.
11
For this reason, men with
impotence
,
infertility
, or decreased libido may wish to avoid this herb. Licorice may also increase both the positive and negative effects of
corticosteroids
such as prednisone and hydrocortisone cream.
12-14
In addition, some evidence suggests that licorice might affect the liver's ability to metabolize other medications as well, but the extent of this effect has not been fully determined.
15

Whole licorice possesses significant estrogenic activity,
16,24
and some evidence indicates that licorice increases risk of premature birth.
17,25
For these reasons, it shouldn't be taken by pregnant or nursing women, or women who have had breast cancer.

Maximum safe doses for young children, nursing women, or those with severe liver or kidney disease have not been established.

It is believed, but not proven, that most or all of the major side effects of licorice are due to glycyrrhizin. For this reason, DGL has been described as entirely safe. However, comprehensive safety studies on DGL have not been reported.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

As of 4/11/2011, additional research published on licorice does not warrant any changes to this article.

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